In the technology of industrial process measurements, especially also in connection with the automation of chemical processes or processing operations, process measuring devices and also field measuring devices are installed on site, thus near to the process, for producing measured value signals representing physical, measured variables.
For the measurement of physical, measured variables, such as e.g. a mass and/or volume flow rate, a density, a viscosity, etc., of media conveyed in pipelines, process measuring devices are often used, which effect the required physical-to-electric conversion of the measured variable by means of a physical-electric measurement pickup and a measuring apparatus electronics connected thereto. The measurement pickup is inserted into the course of a pipeline conveying the medium and thus the medium flows through the pickup during operation. For registering these measured variables, such process measuring devices (referred to herein as inline measuring devices) mostly have a measurement pickup involving at least one measuring tube installed directly into the course of the pipeline. Examples of such inline measuring devices, sufficiently known to those skilled in the art, are described in detail in the U.S. Pat. Nos. 6,691,583, 6,450,042, 6,354,154, 6,352,000, 6,308,580, 6,006,609, 6,003,384, 5,979,246, 5,850,039, 5,796,011, 5,602,345, 5,301,557, 4,768,384, as well as in WO-A 03 095 950, WO-A 03 095 949, or WO-A 95 16 897. Examples of measured variables include a mass flow rate, a density, a viscosity, a pressure or a temperature, or the like, of a liquid, powdered, vaporous or gaseous, process medium.
For a most-often centralized evaluation of the registered, measured variables, process measuring devices of the described kind are, moreover, usually connected together and/or to appropriate process control computers via a data transmission system connected to the measuring apparatus electronics. The measured value signals are sent to other process measuring devices and/or to the process control computers e.g. via (4 to 20 mA-) current loops and/or via digital data busses. Capable of serving as the data transmission system are, in such case, especially serial, fieldbus systems, such as e.g. PROFIBUS-PA, FOUNDATION FIELDBUS, as well as the corresponding transmission protocols. The transmitted, measured value signals can be processed further in the process control computers and visualized as corresponding measurement results e.g. on monitors and/or transformed into control signals for process actuators, such as e.g. solenoid valves, electromotors, etc. For accommodating measuring apparatus electronics, such process measuring devices further include an electronics housing, which, as proposed e.g. in U.S. Pat. No. 6,397,683 or WO-A 00 36 379, can be arranged remote from the process measuring apparatus or connected therewith over a flexible cable or which is, as e.g. shown in EP-A 903 651 or EP-A 1 008 836, arranged directly on the measurement pickup or on a measurement pickup housing separately accommodating the measurement pickup. The electronics housing often then serves also, as shown, for example, in EP-A 984 248, U.S. Pat. No. 4,594,584, U.S. Pat. No. 4,716,770 or U.S. Pat. No. 6,352,000, for additionally accommodating some mechanical components of the measurement pickup, such as e.g. membrane-, diaphragm-, rod-, shell- or tube-shaped deformation, or vibration, members, which mechanically deform during operation; compare, in this connection, the above-mentioned U.S. Pat. No. 6,352,000.
Due to their broad spectrum of application, inline measuring devices with vibration-type measurement pickups have become established for the measurement of media flowing in pipelines. These vibratory pickups utilize at least one measuring tube, which vibrates during operation. The vibrating pickups bring about mechanical reaction forces in the medium flowing therethrough, for example Coriolis forces corresponding to the mass flow rate, inertial forces corresponding to the density of the medium and/or frictional forces corresponding to viscosity. Such inline measuring devices, as well as their manner of operation, are familiar to those skilled in the art and are described in detail e.g. in the already mentioned U.S. Pat. Nos. 6,691,583, 6,450,042, 6,354,154, 6,308,580, 6,006,609, 5,979,246, 5,850,039, 5,796,011, 5,602,345, 5,301,557, 4,876,898, 4,768,384, as well as in WO-A 03 095 950, WO-A 03 095 949, WO-A 02 088 641 or WO-A 95 16 897.
For the conveying of the medium, such vibration-type measurement pickups include, in each case, at least one measuring tube held in a, for example tubular or box-shaped, support frame. The measuring tubes have a curved, or straight, tube segment, which is caused to vibrate in a suitable oscillation mode—driven by an electromechanical exciter arrangement—for producing the aforementioned reaction forces during operation. For registering vibrations of the tube segment, the measurement pickups additionally include a sensor arrangement, which reacts to movements of the vibrating tube segment. The sensor arrangement has physical-electrical, mostly electrodynamic or opto-electronic, oscillation sensors, which deliver oscillation measurement signals representing local oscillations of the measuring tube.
The at least one measuring tube, as well as the exciter and sensor arrangements, are surrounded by a housing cap, which is connected to the support frame, especially welded thereto or integrated therewith. The thus-formed measurement pickup housing serves, besides for holding the at least one measuring tube, among other things also for protecting the measuring tube, and the exciter and sensor arrangements, as well as other internally situated components, from external, environmental influences, such as dust or water spray, and also for suppressing sound emissions of the measurement pickup.
For the case that the inline measuring device is installed as a Coriolis mass flow meter, the measuring apparatus electronics repeatedly determines, among other things, a phase difference between the oscillation measurement signals, which are delivered from two mutually spaced, oscillation sensors, and the measuring apparatus electronics issues at its output a measured value signal, which, in correspondence with the time behavior of the determined phase difference, represents a measured value of the mass flow rate. In addition to this, such inline measuring devices can, as described in the above-referenced WO-A 95/16897, U.S. Pat. No. 4,524,610 or U.S. Pat. No. 4,187,721, measure the instantaneous density of the flowing medium, on the basis of a frequency of at least one of the oscillation measurement signals delivered by the sensor arrangement. Additionally, such inline measuring devices can also directly measure a viscosity and/or a viscosity-density product of the medium located in the vibrating measuring tube; compare, in this connection, especially the U.S. Pat. Nos. 6,651,513, 5,531,126, 5,253,533, 4,524,610 or WO-A 95/16897. Besides this, alone for the purpose of possibly required compensations of temperature effects in the oscillation measurement, most often also a temperature of the medium and/or of individual components of the measurement pickup are directly measured in suitable manner, for example by means of temperature sensors arranged on the measuring tube and/or on the housing.
In the case of using inline measuring devices in applications where the medium to be measured, for example heated hydrocarbon compounds or the like, are to be kept as accurately as possible within a predetermined temperature range, it is often necessary also to control the temperature of the inline measuring device in suitable fashion, for example by the introduction, or withdrawal, of heat. For controlling the temperature of inline measuring devices, thus for the adding, or withdrawal, of heat, especially devices have proven successful, which tie into an appropriate temperature-control piping system installed on site and carrying a suitable temperature-control fluid, such as e.g. water, water vapor, oil, or the like. Such devices for controlling the temperature of inline measuring devices have been available on the market for quite some time.
An apparatus available from the assignee itself—to be considered as fairly representative of temperature control apparatuses common at this time—exhibits, for example, as shown schematically in FIGS. 1 and 2, two heat exchangers, each having a chamber which can be connected to the temperature control piping system. These chambers are mountable opposite to one another externally, by means of suitable securement means, onto the inline measuring device. In this case, due to the principle of measurement, the mounting is directly on the measurement pickup housing. Each of the two heat exchangers has an inner wall contacting the inline measuring device externally flushly, at least in part, and appropriately corresponding to the external contour of the inline measuring device. Welded onto the inner wall is an essentially box-shaped outer wall for forming a chamber therebetween. For the purpose of controlling the temperature of the inline measuring device, the two chambers have temperature-control fluid flowing through them during operation.
A disadvantage of temperature-control devices constructed in this way is, on the one hand, the rather unfavorably designed volume of the chamber containing the temperature-controlling fluid. Size and shape of the illustrated chamber lead, namely, to the fact that the temperature-controlling apparatus exhibits a very great thermal inertia with respect to the ability of temperature changes within the chamber to act on the inner wall, thus a very low response dynamics. Beyond this, considerable dead volume forms within the chamber, where the temperature-controlling fluid scarcely circulates, if at all. Also, there is no studied guidance of the flow of the temperature-controlling fluid. As a result of these factors, such devices mostly have a very low thermal efficiency at relatively low heating/cooling power, as, in fact, confirmed by the experimentally determined temperature plots shown in FIG. 3. Moreover, such devices usually also have a very high weight, which can lie about in the area of 100% of the nominal weight of the inline measuring device whose temperature is to be controlled, thus, at around 100 kg, or even more. Additionally, the rather unfavorably shaped, outer wall requires, with its relatively large surface area, considerable attention to the blocking of heat flow as regards thermal insulation.
A further disadvantage of such temperature control devices lies in the fact that they exhibit a rather low nominal pressure resistance, which, as shown, for example, in FIG. 4 for the above-described apparatus in the case of inline measuring devices of nominal diameter DN≦100 mm, can, moreover, sink considerably with increasing temperature. Beyond this, the large volumes of the chambers, which mostly significantly exceed 20 l, lead to the fact that the applied heat exchangers are subjected to increased demands with respect to their pressure resistance and strength testing. As a result, the use of such devices is often allowable only for applications of relatively low temperatures, for example of below 200° C., and/or of low pressure within the temperature-controlling system, for example pressures below 3 bar.
Each individual temperature-controlling apparatus of the described kind is, consequently, quite complicated, so that it is feasible only for manufacture in small runs, or ever single units.